Not sure if this is related but I had an issue using DB2 and unnamed parameters with SSRS.
With trial and error I found out the following:
Put a ? in place of every usually named parameter e.g.
Select * from SCRATCH.PROD_KPI_REPORT_DATA KPI
(KPI.PRODUCT =? or ? = 'ALL')
(KPI.CHANNEL = ? or ? = 'ALL')
for read only with ur;
Then set up the parameters in REPORT PARAMETERS and throwing away the default entries created that you don't want, i.e. I had 4 Parameter1, Parameter2 etc.
Then back in the dataset, select ... and move to the PARAMETERS tab.
Every ? used appears, I had 4 for example.
Now simply use the drop down to assign your named parameters created in REPORT PARAMETERS. In my example the first 2 ? were assigned to my first named parameter and the second 2 ? to my second named parameter.
Just have to make sure your named parameters are matched to the correct ? order.